Hemp (Cannabis sativa L.), also known as marijuana, is a plant in the Cannabis genus which belongs to the family Cannabaceae, and has important agricultural and medicinal value. The hemp contains a toxic ingredient THC (tetrahydrocannabinol) which can make people to be hallucinated and addicted. The hemp can be used as a drug and has been banned for a long period of time.
The economic and medicinal value of hemp is extremely high, raw hemp dedicated to industrial use is simply referred to as ‘industrial hemp’, and its tetrahydrocannabinol (THC) content in the hemp flowers and leaves in the growth period is less than three-thousandths, so the industrial hemp cannot extract toxic tetrahydrocannabinol or be used directly as drug. Therefore, it can be legally subjected to large-scale cultivation and industrial development and utilization.
At present, more than 500 substances have been separated from hemp plants, among which there are at least 86 cannabinoids. Cannabinoids are a unique class of substances in the hemp plants and main active ingredients in hemp plants. Research on cannabinoids has always been a hotspot in hemp research. The main cannabinoids in hemp plants are tetrahydrocannabinol (THC), cannabinol (CBN), cannabidiol (CBD), cannabigerol (CBG), cannabichromene (CBC), etc., among which the top three account for more than 90% of cannabinoids.
In recent years, research on active ingredients of hemp found that cannabidiol is not neurotoxic and has significant medicinal value. Related pharmacological research has shown that it can hinder the effect of tetrahydrocannabinol on the human nervous system, has pharmacological activities such as anti-spasm, anti-rheumatoid arthritis and antianxiety, and thus, has great industrial development value.
At present, there are some reports in the public information about methods of extracting cannabidiol or extracting cannabidiol-containing industrial hemp oil from industrial hemp. For example, CN104277917A discloses a method and a device for extracting cannabidiol-rich industrial hemp essential oil; and a screener, an oven, and a soaking pool, a rotary evaporator, an ultrasonic stirring tank, a disk centrifuge, a first climbing film evaporator, a proportioning tank, a pressure chromatographic silica gel column, an eluate tank, a second climbing film evaporator, a rotary evaporator, a finished product tank and a solvent recovery tank that are sequentially connected by pipelines are adopted to sequentially perform operation steps of screening, baking, leaching, retreatment, filtration, monitoring, loading, chromatography, concentration and finished production acquisition for the industrial hemp, thereby finally extracting industrial hemp essential oil which is rich in the effective ingredient cannabidiol. CN 105505565 A discloses a method of extracting cannabidiol-rich industrial hemp oil, which uses a supercritical carbon dioxide fluid to extract industrial hemp oil from industrial hemp; and in the extraction process, cooled industrial hemp powder is put into a material vat of an extraction kettle, and CO2 gas is injected into the extraction kettle to keep such temperature and pressure in the extraction kettle that the CO2 gas contacts the raw material in the supercritical state, so that industrial hemp oil and other ingredients in the industrial hemp powder are dissolved in the supercritical fluid, and thus, the fluid containing cannabidiol and other ingredients is subjected to throttling expansion to enter a separation kettle from the extraction kettle to be resolved, thereby obtaining and collecting the industrial hemp oil. CN 105535111 A discloses a preparation method of extracting a cannabidiol-rich hemp extractum from industrial hemp flowers and leaves, which includes the following steps: performing dry heat treatment on hemp flowers and leaves, and obtaining a cannabidiol-rich crude extractum by a subcritical butane extraction technique with ethanol as an entrainer; dissolving the crude extractum in an ethanol solution of a certain proportion, and performing low-temperature winterization; centrifuging or filtering to remove wax; adding activated carbon into the supernate to perform decolorization, and performing filtration treatment; and finally, performing rotary evaporation on the obtained filtrate to remove the ethanol, thereby obtaining the CBD-rich hemp extractum. The prior art CN 103739585 A, which is the closest to the present invention, discloses a technique for extracting cannabidiol (CBD) from industrial hemp; the technique includes the following steps: picking of flowers and leaves, drying, grinding, soaking extraction, and concentration and separation; and through comparative studies, the method of extracting cannabidiol from industrial hemp mentioned in the prior art mainly has the following problems:
1) due to the complexity of cannabinoids in the original plant and the existence of many polarity-like ingredients, the purity of cannabidiol in the final product is not high after extraction and refinement by the traditional method;
2) after extraction and purification, tetrahydrocannabinol, a psychotoxic ingredient, can still be detected, so the product safety cannot be guaranteed, product circulation is limited, and industrial production and applications are affected; and
3) since the solubility of cannabidiol in organic solvents is higher than that in ethanol, in order to increase the yield of cannabidiol, the industry usually uses a toxic organic solvent, such as petroleum ether, n-hexane, dichloromethane or the like, in the technical steps of extraction, leaching, purification and the like, however, the use of such organic solvents may do harm to the environment, and the solvent residues in the final product cannot be completely removed, which also affects the product safety.
Therefore, there is currently an urgent need to provide a method of preparing high-purity tetrahydrocannabinol-free cannabidiol without residues of poor organic solvents. The preparation method should also satisfy the industrial development demands of energy saving, environment friendliness and economy.